Hi Everybody, This will be my second CNC Router build. First being a 500mm Xcarve. I'm about 80% percent done the mechanical build and thought I would make a few notes on how it's been going. First small issue I ran into was the two Y pieces of C-Beam wouldn't sit down flat onto the V-Slot. Turns out the V-Slot doesn't have a bevel on the edges and the end plate bearing sits about .020 proud of the inside surface of the plate. I was puzzled as the X axis C-Beam fit fine, But the C-Beam has a much bigger bevel giving the bearing some clearance. A quick swipe with a half round file once I knew where the Y C-Beams were going to sit took care of the problem. I thought I would mention it to help any one building theres. Second issue I'm having is not being able to get the Wheels to tighten up enough with the 6mm eccentrics on the C-Beam. I read that others were having the problem as well. There is enough play in the fixed side I ended up getting a little preload by loosening and tightening the fixed side back up while I pushed them in with a piece of wood (if that makes any sense?) But it ended up moving the lead screw off center just enough that it sightly binds the lead screw when it at the end of it's range (close to the lead nut) Not sure what to do here other than order some 6mm Eccentrics for the other side, but i'm thinking that will push the lead screw center off that much more. third a final issue I was having was setting the pre load on the twin lead nuts. I found them very tough to tighten as the whole block would turn slightly whenever I tried to tighten them, ending up with a binding lead screw. what I ended up doing was tightening them and then using a long punch to "lightly" tap the blocks straight until I was happy with the preload. I also went with a 1" piece of MDF for the table as I didn't have any luck glueing up two pieces of 1/2. I kept getting a droop on one side of the table when it was done. About 0.025" right where the left bottom zero would have been, So I scrapped it and picked up a piece of 1" MDF and that worked GREAT although its harder to drill the mount holes straight without a guide of some kind. Well thats my $.02! so far. All in all a really well designed kit and has been great to build so far. Have a look at the pictures as it will explain the bearing issue a little better. Thanks, Scott
Oops, designer fault... well spotted and solved Clearcutter. I totally missed it in the model and didn't notice it on my build as I flipped the end plates to put the lead screws in tension to see how it goes, so the bearing are on the outside on my build. Thanks for spotting it..
Moag, So by putting the lead screws in tension your trying to eleviate some whipping? Hows it working?
That was the plan, though not easy with the current lengths of the lead screws unless you cut down the c-beam lengths from standard sizes to accommodate a better technique of putting them in tension; with the added bonus of being able to fit some hand cranks. Which I'm thinking of doing at some stage to get less twist in the X C-beam, as I think this is weakest part in the design in real life and while I'm at it... - fill the beams with engine block filler - double up the Z gantry with double wheels - slip in some support wheels under the table - Add a bottom table to the bottom double Y gantries with a cut out in the top so I can edge mill aluminium moulds. - among other mods. So if and when I do that mod, I should be able to give a more objective opinion on how effective it is.
My cunning plan to eliminate twist in the X beam, with my future "CBeam OneByOne", is to add 2 extra 40 x 20mm cross members to the X gantry columns, flat side down. One will be about 100mm above the CBeam, and the other about 100mm below the CBeam. Each will have a 1000mm MGN12 Linear Motion Guideway Rail attached to the edge of the 40 x 20mm and attached to a longer Z axis 500mm Linear Actuator. Obviously the Gantry uprights will be extended to accommodate the additional space required, as well as beefing up the base of them to avoid flex in those as well! So the general idea, is to remove any chance of twist in the X axis, by causing the stress to be transfered and cancelled out, by the two cross members above and below. Gray
Sounds like a good plan GrayUK... Just a quick screen capture of a old design with some ideas for all...
Interesting stuff! I like the connector between the two Y plates as well as the wheels. I was thinking about those linear motion guideway rails as well for the Y in about the same location as those wheels. One on either side of the Y C-beams at the edges of the table. It would eliminate any twisting of the table.
My Y C-Beams are just a touch longer by 1 or 2 mm so I never noticed the Bearing problem, They sit down fine but I will check to see if my bearings do sit proud. I know one thing for sure there is not much clearance for the Collar/Grub Screw... I had the grub screw hitting the V-slot when rotating until I filed the a flat spot on the lead screw so the grub screw went in a little further. Here is something I have noticed, If I look along the edge of the table in the X direction I can see quite a Dip in the middle between the two Y Gantry's and I was thinking about building a another complete Y Gantry (NON Motorized) to sit in between the existing ones, it could also be tied together with the other two like in the above picture @Moag posted. I am using full MDF at the moment but certainly would like to upgrade to Aluminium Plate which may help in the sag area too. Glenn.
Glenn, That's why I scrapped my first glued up table. The 1" MDF seems to be MUCH better. I was thinking that instead of an aluminum table which would have to be milled flat, that just some aluminum supports added to the 1" MDF would really stiffen it up. It wouldn't take much, one or two lengths of channel either sitting into a milled slot underneath the table or secured to the front and rear edge of the table.
